C. Gould

Addition spectrum of a lateral dot from Coulomb and spin-blockade spectroscopy

Transport measurements are presented on a class of electrostatically defined lateral dots within a high mobility two dimensional electron gas (2DEG). The new design allows Coulomb Blockade(CB) measurements to be performed on a single lateral dot containing 0, 1 to over 50 electrons. The CB measurements are enhanced by the spin polarized injection from and into 2DEG magnetic edge states. This combines the measurement of charge with the measurement of spin through spin blockade spectroscopy. The results of Coulomb and spin blockade spectroscopy for first 45 electrons enable us to construct the addition spectrum of a lateral device. We also demonstrate that a lateral dot containing a single electron is an effective local probe of a 2DEG edge.

Readout of a single electron spin based quantum bit by current detection

Abstract We present experimental and theoretical results demonstrating the readout of a single spin based quantum bit by current detection. The quantum bit has been built by isolating a single electron spin in a lateral dot with a tunable number of electrons. The spin state of the dot was read from the current amplitude resulting from the injection of spin polarized electrons. The current amplitude showed a systematic dependence on the spin state of the dot controlled by the number of electrons.

Spin polarized injection into a quantum dot by means of the spatial separation of spins

Abstract We describe transport measurements on a small lateral dot involving spin polarized injection and detection. The novel layout of the lateral dot allows its electron occupation number to be reduced to 0 from 60 while maintaining operating tunneling barriers. The spin polarized injection occurs above (0.4 T ) due to the presence of spin resolved edge states in the two dimensional electron gas which form the leads to the quantum dot. We demonstrate the consequences of spin polarized leads by focusing on two spin properties of the quantum dot close to filling factor, ν , 2. Firstly, we illustrate an alternating odd/even occupation number effect due to spin blockade through current readout at ν =2. Secondly, we detect spin transitions directly at fixed electron number in the quantum dot as the magnetic field is lowered away from ν =2. The experimental results are explained by a comparison to theoretical calculations of the ground states in the different regimes. The current readout process is one of the requirements of a quantum dot based spin qubit quantum computer.

Correlations effects in few-electron quantum dots between ν=2 and 1

Abstract We investigate correlation effects in few-electron lateral quantum dots between filling factor ν=2 and 1. The correlations are the non-trivial spin depolarization events associated with the evolution of the total spin of the droplet with increasing magnetic field. We monitor the spin evolution by measurements of coulomb blockade (CB) peaks on lateral quantum dot devices containing from 5 to 20 electrons. Measurements are made as a function of the magnetic field, temperature, and source–drain bias. The temperature and high source–drain bias dependence of the CB peaks in the vicinity of the spin-flip are consistent with spin depolarization events due to electronic correlations.

Magnetoconductance of a few-electron open quantum dot

Abstract Magnetoconductance of a small open lateral dot is studied both theoretically and experimentally for the conditions when the dot contains down to ∼15 electrons. We confirm the existence of a new regime for open dots in which the transport through the structure occurs through individual eigenstates of the corresponding closed dot. In particular, at low magnetic fields the characteristic features in the conductance are related to the underlying eigenspectrum shells. When the number of modes in the leads is reduced more detailed structures within the shells due to single eigenlevels becomes discernible. At higher fields Landau level condensation is evident as well as the crossing of levels collapsing to the different Landau levels.

Spin depolarization in quantum dots

We have performed single electron spectroscopy experiments on single lateral quantum dots. We demonstrate that the lateral nature of the tunneling as well as the properties of the 2DEG leads can be used to extract new information in the spin-flip regime. Calculations confirm that one needs to go beyond the Hartree-Fock approximation and include correlation effects to explain the experimental observations. The results are found to be consistent with the presence of spin depolarization events at the spin-flips.